Inkjet printer having printhead plumbed for optimized color mixing

ABSTRACT

An inkjet printer including an inkjet printhead positioned relative to a media feed direction. The printhead has a plurality of color planes for ejecting different inks, each color plane including a nozzle row defined in a nozzle face of the printhead, and each nozzle in a respective color plane being supplied with a same ink. The printhead is plumbed such that a first color plane positioned furthest upstream with respect to the media feed direction ejects yellow ink and a second color plane neighboring the first color plane ejects black ink.

PRIORITY

This application claims priority under 35 U.S.C. 119(e) to U.S.provisional application No. 61/537,063 entitled “PRINTER FOR MINIMIZINGADVERSE MIXING OF HIGH AND LOW LUMINANCE INKS AT NOZZLE FACE OF INKJETPRINTHEAD,” filed on Sep. 21, 2011, the content of which is herebyexpressly incorporated by reference in its entirety for all purposes.

FIELD OF THE INVENTION

This invention relates to inkjet printing and methods for improvingprint quality. It has been developed primarily for minimizing adversecolor mixing on nozzle plates of inkjet printheads.

BACKGROUND OF THE INVENTION

The present Applicant has developed a plethora of thermal bubble-formingprintheads and thermal bend-actuated printheads. The Applicant's thermalbubble-forming printheads include those with suspended heater elements(as described in, for example, U.S. Pat. No. 6,755,509; U.S. Pat. No.7,246,886; U.S. Pat. No. 7,401,910; and U.S. Pat. No. 7,658,977, thecontents of which are incorporated herein by reference) and those withembedded or bonded heater elements (as described in, for example, U.S.Pat. No. 7,377,623; U.S. Pat. No. 7,431,431; US 2006/250453; and U.S.Pat. No. 7,491,911, the contents of which are incorporated herein byreference). The Applicant's thermal bend-actuated printheads typicallyhave movable paddles defined in a nozzle plate of the printhead (asdescribed in, for example, U.S. Pat. No. 7,926,915; U.S. Pat. No.7,669,967; and US 2011/0050806, the contents of which are incorporatedherein by reference).

The Applicant's Memjet® printheads are characterized by a relativelyhigh nozzle density compared to commercially-available printheads.Memjet® printheads typically comprise a plurality of color planes with apair of offset nozzle rows in each color plane. A key advantage ofMemjet® printheads is the relatively narrow print zone resulting fromintegration of a plurality of color planes on each printhead integratedcircuit. The color planes of the Memjet® printhead are spaced closelytogether, which obviates any alignment problems between the color planesduring dot-on-dot printing. By contrast, widely spaced color planesnecessitate complex media feed mechanisms to achieve proper alignment,adding to the complexity of other known pagewidth printing systems (e.g.HP Edgeline).

Typically, a distance between nozzles rows from neighboring color planesin a Memjet® printhead is in the range of 25 to 200 microns or 50 to 100microns. This close spacing of color planes produces problems which areunique to such printheads. A significant problem of closely spacednozzle rows from different color planes is one of color mixing on thenozzle plate of the printheads. If, for example, black ink mixes into ayellow ink on the nozzle plate, then this may adversely affect printquality as well as impacting on printhead maintenance routines. Thepresent Applicant has identified two mechanisms which manifest inadverse ink mixing on the nozzle plate: ink wetting onto the nozzleplate; and fibres or particulates bridging between rows of nozzles.

Hitherto, the problem of ink mixing on the nozzle plate of inkjetprintheads has been addressed in the art by applying hydrophobic surfacetreatments to the nozzle plate. For example, the present Applicant hasdescribed nozzle plates having a coating of a hydrophobic siloxanepolymer, which is applied during MEMS fabrication of the printhead (see,for example, U.S. Pat. No. 7,938,974; U.S. Pat. No. 7,669,967, thecontents of which are herein incorporated by reference). However, suchcoatings add to the cost and complexity of printhead fabrication.Moreover, they do not control a direction of color mixing so as to favoracceptable color mixing over adverse color mixing.

It would be desirable to provide a means for minimizing adverse colormixing on inkjet nozzle plates, which does not rely on nozzle platecoating treatments. Alternatively, it would desirable to provide a meansfor minimizing adverse color mixing on inkjet nozzle plates, whichcomplements and/or improves the effectiveness of existing nozzle platecoating treatments.

SUMMARY OF THE INVENTION

In a first aspect, there is provided an inkjet printer comprising:

an inkjet printhead comprising a plurality of color planes for ejectinga plurality of different inks, each color plane comprising at least onenozzle row defined in a nozzle face of said printhead, each nozzle in arespective color plane being supplied with a same ink, wherein saidprinthead is plumbed such that a first color plane ejecting a first inkhaving a relatively low luminance is sandwiched between second and thirdcolor planes ejecting respective second and third inks having arelatively high luminance; and

a plurality of ink reservoirs in fluid communication with the printhead,said ink reservoirs containing the first, second and third inks,

wherein an amount of surfactant in the first ink is at least 0.4 wt %greater than an amount of surfactant in the second and third inks.

Typically, the first ink is a color ink, while the second and third inksare black inks. As used herein, the term “color ink” refers to anynon-black ink used in inkjet printing. Typical examples of color inksare cyan, magenta, yellow, red, green and blue, as well as light cyan,light magenta and spot colors. Other types of “color inks” may includeinfrared inks, ultraviolet inks, metallic inks etc. An infrared ink, forexample, is defined herein as a “color ink” even though it may havevirtually no color. In the context of the present disclosure, color inkssuch as ‘light cyan’ and ‘cyan’ are not considered to be “differentcolor inks”, because their intermixing on the nozzle face does have aserious visual impact. Likewise, ‘light magenta’ and ‘magenta’ are notconsidered to be different color inks, because their intermixing on thenozzle plate does not have a serious visual impact.

The printer according to the first aspect is based on the combination ofa unique ink set and a unique plumbing arrangement in an inkjetprinthead. This combination enables control of the flow of inks acrossthe nozzle plate of the printhead in order to minimize the effects ofadverse color mixing. Notably, the printer does not attempt to preventall color mixing on the nozzle plate. In terms of producing adverseprint defects, the visual impact of inks mixing on the nozzle plate isnot equal. For example, the mixing of cyan, magenta or yellow ink intoblack ink does not produce highly undesirable print defects.Essentially, the black ink remains black irrespective of whether a colorink has been mixed with the black ink. However, the mixing of black inkinto cyan, magenta or yellow ink produces highly undesirable printdefects, because the black ink seriously affects the visual appearance(i.e. hue and chroma) of color inks. It is this type of undesirablemixing which the present invention aims to minimize.

Initially, it was envisaged by the present inventors that control ofinks across the nozzle plate could be achieved by making use of theknown Marangoni effect—that is, the propensity of fluids having a lowsurface tension to flow towards regions having a high surface tension.However, it was found that surface tension differences between inks wasnot sufficient to control their flow across the nozzle plate. Even when,for example, a black ink had a significantly higher surface tension thancolor inks, the black ink was still observed to flow into color inks onthe nozzle plate. Thus, it appeared that surface tension gradients alonewere not effective in controlling ink flow across the nozzle plate.

However, it was found, surprisingly, that controlling an amount ofsurfactant in each ink was highly effective in controlling ink flowacross the nozzle plate. In particular, it was found that it wasnecessary for a color ink to contain at least 0.4 wt. % more surfactantthan the black ink in order to minimize the flow of black ink into thecolor inks on the nozzle plate. Based on this observation, the plumbingorder of the printhead and the surfactant concentration in each ink ofan ink set may be optimized so as to minimize adverse color mixing onthe nozzle face of the printhead.

In connection with the first aspect described above, the printhead isoptionally plumbed such that each color plane ejecting one of therelatively low luminance inks (e.g. color ink) has at least oneneighboring color plane ejecting a relatively high luminance ink (e.g.black ink).

Optionally, the color planes of the printhead are arranged in analternating sequence of black ink and color inks.

Optionally, the printhead comprises five color planes for ejecting blackink, a first color ink, a second color ink and a third color ink,wherein the color planes are plumbed in the sequence: first colorink-black ink-second color ink-black ink-third color ink e.g. CKMKY;MKCKY; MKYKC; RKGKB; GKRKB; RKBKG etc.

Optionally, each color ink is selected from the group consisting of:cyan, magenta and yellow. Alternatively or additionally, each color inkmay be selected from the group consisting of: red, green and blue.Alternatively or additionally, each color ink may be selected from thegroup consisting of: ultraviolet inks and infrared inks, which may becolorless or virtually colorless to the human eye.

Optionally, the inks are dye-based aqueous inks.

Optionally, the inks are pigment-based aqueous inks.

Optionally, the relatively high luminance ink (e.g. black ink) has ahigher surface tension than each relatively low luminance ink (e.g.color ink). Typically, the black ink has a surface tension at 25° C. inthe range of 38 to 43 mN/m and each color ink has a surface tension at25° C. in the range of 30 to 41 mN/m.

Optionally, the amount of surfactant in each color ink is at least 0.6wt. % greater than the amount of surfactant in the black ink.Optionally, each color ink contains from 0.4-1.2 wt. % more surfactantthan the black ink. Typically, the black ink contains 0.1 to 0.4 wt. %surfactant while each color ink contains 0.6 to 1.5% surfactant.

Each color plane of the printhead may comprise one or more nozzle rows.For example, a color plane may comprise 1, 2, 3 or 4 nozzle rows, whichall receive and eject the same ink. Optionally, each color planecomprises a pair of respective nozzle rows, which usually containnozzles offset from each other. The distance between nozzle rows of thesame color plane is usually less than the distance between nozzle rowsfrom neighboring color planes.

The color planes are spaced apart transversely across the printhead. Thedistance between nozzle rows from neighboring color planes is typicallyless than 200 microns or less than 100 microns. Optionally a distancebetween nozzle rows from neighboring color planes is in the range of 30to 180 microns, optionally in the range of 40 to 150 microns, oroptionally in the range of 50 to 100 microns. The close spacing betweenneighboring color planes is particularly problematic in terms of colormixing on the nozzle face.

Optionally, the nozzle face is defined by a nozzle plate comprised of aceramic material. Optionally, the nozzle plate is comprised of amaterial selected from the group consisting of: silicon oxide, siliconnitride and silicon oxynitride. Ceramic nozzle plates are very robustand suitable for MEMS fabrication of printheads. However, ceramics ofthis type are relatively wetting and potentially exacerbate the problemof color mixing, especially with closely spaced color planes. It is aparticular advantage of the present invention that adverse color mixingis minimized even on relatively wetting nozzle plates. However, thepresent invention is equally suitable for use with other nozzle faces,for example, nozzle plates coated with a hydrophobic polymer coating asdescribed in U.S. Pat. No. 7,938,974, the contents of which are hereinincorporated by reference.

Optionally, the printhead is a stationary pagewidth printhead, such asthose described hereinbelow. The printhead may be comprised of aplurality of printhead integrated circuits butted end-on-end across apagewidth. However, the present invention is equally suitable for usewith other types of printhead, especially multi-color printheads withclosely spaced color planes (i.e. less than 500 microns or less than 200microns).

In a second aspect, there is provided a printhead suitable for use inthe printer described in connection with the first aspect. Accordingly,the second aspect provides an inkjet printhead comprising a plurality ofcolor planes for ejecting a plurality of different inks, each colorplane comprising at least one nozzle row defined in a nozzle face ofsaid printhead, each nozzle in a respective color plane being suppliedwith a same ink, wherein said printhead is plumbed such that a firstcolor plane ejecting a non-black ink is sandwiched between a pair ofcolor planes ejecting black ink.

Optional features described above in connection with the first aspectare, of course, equally applicable to the printhead according to thesecond aspect.

In a third aspect, there is provided an ink set suitable for use in theprinter described above in connection with the first aspect.Accordingly, the third aspect provides an ink set for minimizing adversecolor mixing at a nozzle plate of an inkjet printhead, said ink setcomprising a plurality of aqueous inks including a relatively highluminance ink and one or more relatively low luminance inks, each ofsaid inks comprising a surfactant, wherein an amount of surfactant inthe first relatively high luminance ink is at least 0.4 wt % greaterthan an amount of surfactant in said relatively low luminance inks.

As described in more detail below, each ink of the ink set is formulatedas a dye or pigment contained in an aqueous-based ink vehicle. Specificexamples of suitable dyes and pigments are described below. Preferably,each ink of the ink set is a dye-based ink. A typical ink vehiclesuitable for use in the present invention may comprise one or more of: 8to 15 wt. % ethylene glycol; 6 to 12 wt. % 2-pyrrolidinone; 1 to 5 wt. %glycerol; 1 to 5 wt. % 1-propanol; and from 2 to 20 wt % of at least oneoxyalkylene compound selected from the group consisting of: diethyleneglycol, triethylene glycol, tetraethylene glycol and pentaethyleneglycol.

Optionally, each ink of the ink set comprises only one surfactant, whichis typically a nonionic surfactant. Optionally, the nonionic surfactantis ethoxylated 2,4,7,9-tetramethyl-5-decyne-4,7-diol (Surfynol® 465).

Optionally, each relatively low luminance ink (e.g. color ink) of theink set comprises from 0.1 to 0.3 wt. % of the surfactant.

Optionally, the relatively high luminance ink (e.g. black ink) of theink set comprises from 0.6 to 1.4 wt. % of the surfactant.

Optionally, each ink of the ink set comprises from 2 to 8 wt. % of adye.

In a fourth aspect, there is provided a kit (e.g. an inkjet printingsystem) comprising: an inkjet printhead comprising a plurality of colorplanes for ejecting a plurality of different inks, each color planecomprising at least one nozzle row defined in a nozzle face of saidprinthead, each nozzle in a respective color plane being supplied with asame ink, wherein said printhead is plumbed such that a first colorplane ejecting a first ink having a relatively low luminance issandwiched between second and third color planes ejecting respectivesecond and third inks having a relatively high luminance; and

-   a plurality of ink reservoirs for installation in the printer, said    ink reservoirs containing the first, second and third inks,-   wherein an amount of surfactant in the first ink is at least 0.4 wt    % greater than an amount of surfactant in the second and third inks.

In a fifth aspect, there is further provided the novel use of an ink setfor minimizing adverse color mixing at a nozzle face of an inkjetprinthead. The ink set employed in the fifth aspect comprises aplurality of dye-based or pigment-based aqueous color inks and adye-based or pigment-based aqueous black ink, each of the inkscomprising a surfactant, wherein an amount of surfactant in each colorink is at least 0.4 wt % greater than an amount of surfactant in theblack ink. The printhead defined in the fifth aspect is typically asdescribed above in connection with the second aspect.

As described above, the present invention may be used in connection withink sets comprising black ink and color inks. More generally, thepresent invention is applicable to any ink set, where the visual impactof a low luminance ink mixing with a high luminance ink is not severe.

The luminance of CMY inks on white paper are as follows: C (30%), M(59%) and Y (11%). Black (K) nominally has 100% luminance on whitepaper. An “invisible” ink, such as an invisible infrared or ultravioletink, nominally has a luminance of 0% on white paper.

Since yellow has a relatively low luminance, then it is highly desirableto avoid mixing either cyan or magenta inks into yellow ink, becausethis would have a highly deleterious visual impact. Conversely, mixingyellow ink into either magenta or cyan inks has less visual impact,although there will still of course be some visual impact.

Making use of the relatively high luminance of black and magenta, andthe relatively low luminance of yellow and IR inks, then a number ofoptimal printhead configurations and ink sets would be readily apparentto the person skilled in the art.

For example, a printhead with four color planes may be optimallyconfigured as follows: CKYM, with a complementary ink set in which cyanand yellow inks have at least 0.4 wt. % more surfactant than black andmagenta inks. Thus, cyan may mix into black with minimal visual impact,and yellow may mix into black or magenta with minimal visual impact.However, mixing of black into cyan or yellow is minimized, and mixing ofmagenta into yellow is minimized.

A Netpage printer (see, for example, U.S. Pat. No. 6,987,573, thecontents of which are incorporated herein by reference) may comprise aprinthead with five color planes optimally configured as follows:CKYM(IR) or YM(IR)KC. In each configuration, the higher luminance inks(M and K) are sandwiched between lower luminance inks (Y, IR and C). Thecomplementary ink set is formulated such that the cyan, IR and yellowinks have at least 0.4 wt. % more surfactant than the magenta and blackinks.

A printer (e.g. photo printer) having three color planes may beoptimally configured as CYM, with a complementary ink set in which theyellow ink has at least 0.4 wt. % more surfactant than the cyan andmagenta inks.

A photo printer having five color planes may be optimally configured asC1C2YM2M1, with a complementary ink set in which the yellow ink has atleast 0.4 wt. % more surfactant than neighboring cyan and magenta inks(C2 and M2). In the case of this photo printer, C1 and C2 (as well as M1and M2) may be redundant color planes. In other words, C1 and C2 ejectidentical cyan inks, and M1 and M2 eject identical magenta inks. Theredundancy in these color planes assists in minimizing the visual impactof yellow ink mixing into the neighboring cyan and magenta color planes,especially in combination with ‘dot-at-time’ redundancy (as described inU.S. Pat. No. 7,465,017, the contents of which are herein incorporatedby reference), wherein pairs of redundant color channels contributeequally to each line of printed dots. Alternatively, one of the cyancolor planes (C1 or C2) may be light cyan and one of the magenta colorplanes (M1 or M2) may be light magenta. Even in the case where C1 and C2(and M1 and M2) eject non-identical inks, such as cyan and light cyan,the visual impact of yellow mixing into cyan and magenta color planes isstill minimal.

In an sixth aspect, there is provided inkjet printhead comprising aplurality of color planes for ejecting different color inks, each colorplane comprising at least one nozzle row defined in a nozzle face of theprinthead, wherein the printhead is plumbed such that a color planeejecting yellow ink is sandwiched between a color plane ejecting magentaink and a color plane ejecting cyan ink.

Optionally, the printhead has redundant color planes ejecting magentaand cyan inks.

Optionally, the printhead comprises five color planes for cyan, magentaand yellow inks, wherein the color planes are plumbed in the sequence:first magenta-second magenta-yellow-first cyan-second cyan.

Other optional features of the printhead according to the eighth aspectare as described above in connection with the first aspect.

In a seventh aspect, there is provided an inkjet printer comprising:

-   -   the inkjet printhead according to the sixth aspect; and    -   cyan, magenta and yellow ink reservoirs, each being in fluid        communication with at least one color plane of the printhead,        wherein an amount of surfactant in the yellow ink is at least        0.4 wt % greater than an amount of surfactant in the magenta and        cyan inks.

In an eighth aspect, there is provided an ink set for minimizing adversecolor mixing at a nozzle plate of an inkjet printhead, the ink setcomprising a cyan ink, a magenta ink and a yellow ink, each of the inkscomprising a surfactant, wherein an amount of surfactant in the yellowink is at least 0.4 wt % (or at least 0.6 wt. %) greater than an amountof surfactant in the magenta and cyan inks.

Optional features of ink vehicles for inks contained in ink setaccording to the eighth aspect are typically as described above inconnection with the ink set according to the third aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present invention will now be described byway of example only with reference to the accompanying drawings, inwhich:

FIG. 1 is a plan view of a printhead comprised of abutting printheadintegrated circuits;

FIG. 2 is plan view of a single printhead integrated circuit;

FIG. 3 shows schematically the arrangement of color planes and nozzlerows in the printhead integrated circuit shown in FIG. 2;

FIG. 4 is a magnified front perspective view of the printhead integratedcircuit shown in FIG. 2;

FIG. 5 is a magnified rear perspective view of the printhead integratedcircuit shown in FIG. 2;

FIG. 6 is a cutaway perspective through one color plane of the printheadintegrated circuit shown in FIG. 2;

FIG. 7 is an exploded perspective view of a printhead assembly;

FIG. 8 is a plan view of fluidic connections to a printhead integratedcircuit in the printhead assembly shown in FIG. 7;

FIG. 9 is a magnified view of the fluidic connection shown in FIG. 8;

FIG. 10 is a perspective view of a printhead cartridge;

FIG. 11 is a perspective view of the printhead cartridge shown in FIG.10 with a protective casing removed;

FIG. 12 is an exploded perspective view of the printhead cartridge shownin FIG. 10;

FIG. 13 is a front perspective of a print engine with an installedprinthead cartridge;

FIG. 14 is a front perspective of the print engine shown in FIG. 13 withthe printhead cartridge removed;

FIG. 15 is a rear perspective the print engine shown in FIG. 13including ink delivery components;

FIG. 16 is a schematic overview of an ink delivery system for a inkjetprinter.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is particularly suitable for use with theApplicant's Memjet® printheads, which comprise closely spaced colorplanes on a single printhead. As foreshadowed above, such printheads aremore prone to adverse color mixing the nozzle face than other prior artprintheads. However, it will be appreciated that the present inventionis suitable for use in any printhead where it is desirable to avoidadverse color mixing between different color planes on the nozzle face.

Pagewidth Printhead and Printer

Referring to FIG. 1, the Memjet® printhead 10 is a pagewidth printheadcomprised of a plurality of printhead integrated circuits (ICs) 100butted end-on-end. Each printhead integrated circuit 100 typically has alength of about 20 mm. The number of butting printhead ICs 100 in aparticular printhead will, of course, depend on the type of printer. Forexample, a 4″ printhead (suitable for photo or label printing) typicallycomprises five abutting ICs 100, as shown in FIG. 1. An A4 printhead(suitable for home and office use) typically comprises eleven abuttingprinthead ICs 100. More printhead ICs are obviously employed in awide-format printhead. The present invention is not limited to anyparticular width of printhead.

The Memjet printhead 10 is typically comprised of five color planes 1,2, 3, 4 and 5 spaced apart transversely across the printhead in a paperfeed direction. Each color plane comprises a pair of offset nozzle rows,which extend longitudinally along the length of the printhead. Forexample, the color plane 1 comprises nozzle rows 1 a and 1 b, as shownmore clearly in FIGS. 2 and 3. Likewise, color plane 2 comprises nozzlerows 2 a and 2 b; color plane 3 comprises nozzle rows 3 a and 3 b etc.Each color plane is characterized in that all nozzles 102 in the samecolor plane are supplied with and eject the same ink from a common inkreservoir.

Each of the five color planes 1, 2, 3, 4 and 5 of the printhead 10 mayeject a different colored ink. However, the Memjet® printhead 10 usuallyincorporates at least some redundancy in the color planes. For example,there may be a two color planes ejecting black ink, while the otherthree color planes eject cyan, magenta and yellow ink, respectively.Redundancy helps to improve overall print quality by improving opticaldensity and minimizing the visual impact of defective nozzles (see U.S.Pat. No. 7,465,017). Of course, redundant color channels usually receiveink from the same bulk ink reservoir of a printer—this ink is merelychanneled into redundant color planes of the printhead.

Referring to FIG. 3, a distance d between nozzle rows from neighboringcolor planes (e.g. nozzle row 1 b and 2 a) is about 73 microns in theMemjet® printhead 10. Hence, there is potential for intermixing ofdifferent color inks across the nozzle face 101 of the printhead 10between neighboring color planes. Adverse color mixing across the nozzleface 101 is exacerbated when the nozzle face is defined by a relativelywetting nozzle plate material, such as silicon nitride or silicon oxide.

A nozzle pitch between neighboring nozzles in the same nozzle row is31.75 microns. The pair of nozzle rows in a same color plane are offsetby a distance of 15.875 microns along a longitudinal axis of theprinthead, such that one nozzle row prints ‘even’ dots of a line and theother nozzle row prints ‘odd dots’ of a line. In this way, the Memjetprinthead achieves a printed dot-spacing of about 15.875 microns in eachline of print, or about 1600 dpi.

Referring to FIGS. 1, 2 and 4, it will be seen that in regions whereabutting printhead ICs 100 are joined, there is a displaced (or dropped)triangle 107 of nozzle rows. These dropped triangles 107 allow printheadICs 100 to be joined, whilst effectively maintaining a constant nozzlepitch along each row. This arrangement also ensures that more silicon isprovided at the edge of each printhead IC 100 to ensure sufficientlinkage between butting ICs.

A timing device (not shown) is used to delay firing nozzles 102 in thedropped triangles 107, as appropriate. Whilst control of the operationof the nozzles 102 is performed by a printhead controller (“SoPEC”)device, compensation for the dropped rows of nozzles may be performed byCMOS circuitry in the printhead, or may be shared between the printheadand the SoPEC device. A full description of the dropped nozzlearrangement and control thereof is contained in U.S. Pat. No. 7,390,071,the contents of which are herein incorporated by reference.

Referring now to FIG. 5, there is shown an opposite backside face of theprinthead integrated circuit 100. Ink supply channels 110 are defined inthe backside of the printhead IC 100, which extend longitudinally alongthe length of the printhead IC. These longitudinal ink supply channels110 meet with nozzle inlets 112, which fluidically communicate with thenozzles 102 in the frontside. Each of the five ink supply channels 110corresponds with one of the color planes of the printhead, such that oneink supply channel supplies ink to the pair of nozzle rows contained inone color plane.

FIG. 6 is a cutaway perspective of part of a printhead IC showingfluidic communication between a nozzle 102, a nozzle inlet 112 and abackside ink supply channel 110. As shown in FIG. 6, the nozzle 102ejects ink via a suspended bubble-forming heater element (as describedin, for example, U.S. Pat. No. 6,755,509; U.S. Pat. No. 7,246,886; U.S.Pat. No. 7,401,910; and U.S. Pat. No. 7,658,977, the contents of whichare incorporated herein by reference). However, other types of nozzleactuation are equally suitable for use in the printheads describedherein. For example, nozzle actuation may be via an embedded heaterelements (as described in, for example, U.S. Pat. No. 7,377,623; U.S.Pat. No. 7,431,431; US 2006/250453; and U.S. Pat. No. 7,491,911, thecontents of which are incorporated herein by reference). Alternatively,the Applicant's thermal bend-actuated printheads typically have movablepaddles defined in a nozzle plate of the printhead (as described in, forexample, U.S. Pat. No. 7,926,915; U.S. Pat. No. 7,669,967; and US2011/0050806, the contents of which are incorporated herein byreference).

Returning to FIG. 5, the longitudinally extending backside ink supplychannels 110 are divided into sections by silicon bridges or walls 116.These walls 116 provide the printhead IC 100 with additional mechanicalstrength in a transverse direction relative to the longitudinal channels110.

Ink is supplied to the backside of each printhead IC 100 via an inksupply manifold in the form a two-part LCP molding. Referring to FIGS. 7to 10, there is shown an exploded view of an A4 printhead assemblycomprising eleven printheads IC 100, which are attached to the inksupply manifold via an adhesive film 120.

The ink supply manifold comprises a main LCP molding 122 and an LCPchannel molding 124 sealed to its underside. The printhead ICs 100 arebonded to the underside of the channel molding 124 with the adhesive ICattach film 120. The upperside of the LCP channel molding 124 comprisesfive LCP main channels 126, which connect with respective ink inlets 127and ink outlets 128 in the main LCP molding 122. The ink inlets 127 andink outlets 128 fluidically communicate with ink tanks and an ink supplysystem, which supplies ink to the printhead at a predeterminedhydrostatic pressure.

The main LCP molding 122 has a plurality of air cavities 129, whichcommunicate with the LCP main channels 126 defined in the LCP channelmolding 124. The air cavities 129 serve to dampen ink pressure pulses inthe ink supply system.

Referring to FIG. 8, at the base of each LCP main channel 126 are aseries of ink supply passages 132 leading to the printhead ICs 100. Theadhesive film 120 has a series of laser-drilled supply holes 134 so thatthe backside of each printhead IC 100 is in fluid communication with theink supply passages 132.

The ink supply passages 132 are arranged in a series of five rows. Amiddle row of ink supply passages 132 feed ink directly to the backsideof the printhead IC 100 through laser-drilled holes 134, whilst theouter rows of ink supply passages 132 feed ink to the printhead IC viamicromolded channels 135, each micromolded channel terminating at one ofthe laser-drilled holes 134.

FIG. 9 shows in more detail how ink is fed to the backside ink supplychannels 110 of the printhead ICs 100. Each laser-drilled hole 134,which is defined in the adhesive film 120, is aligned with acorresponding ink supply channel 110. Generally, the laser-drilled hole134 is aligned with one of the transverse walls 116 in the channel 110so that ink is supplied to a channel section on either side of the wall116. This arrangement reduces the number of fluidic connections requiredbetween the ink supply manifold and the printhead ICs 100.

To aid in positioning of the ICs 100 correctly, fiducials 103A areprovided on the surface of the ICs 100 (see FIG. 4). The fiducials 103Aare in the form of markers that are readily identifiable by appropriatepositioning equipment to indicate the true position of the IC 100 withrespect to a neighbouring IC. The adhesive film 120 has complementaryfiducials 103B, which aid alignment of each printhead IC 100 withrespect to the adhesive film during bonding of the printhead ICs to theink supply manifold. The fiducials 103A and 103B are strategicallypositioned at the edges of the ICs 100 and along the length of theadhesive IC attach film 120.

Returning now to FIG. 4, the printhead IC 100 has a plurality of bondpads 105 extending along one of its longitudinal edges. The bond pads105 provide a means for receiving data and/or power from the printheadcontroller (“SoPEC”) device to control the operation of the inkjetnozzles 102. The bond pads 105 are connected to an upper CMOS layer ofthe printhead IC 100. As shown in FIG. 6, each MEMS nozzle assembly isformed on a CMOS layer 113, which contains the requisite logic and drivecircuitry for firing each nozzle.

Referring again to FIG. 7, a flex PCB 140 bends around the main LCPmolding 122 and has terminals wirebonded to the bond pads 105 of theprinthead ICs 100. Wirebonding arrangements between the flex 140 PCB andthe bond pads 105 are described in more detail in U.S. Pat. No.7,824,013, the contents of which is herein incorporated by reference.

A paper guide 148 is mounted on an opposite side of the LCP molding 122,with respect to the flex PCB 140, and completes the printhead assembly130.

The printhead assembly 130 is designed as part of a user-replaceableprinthead cartridge 20, which can be removed from and replaced in aprint engine of an inkjet printer. Hence, the flex PCB 140 has aplurality of contacts 146 enabling power and data connections toelectronics, including the SoPEC device, in the printer body.

FIG. 10 is a perspective of the complete printhead cartridge 20. Theprinthead cartridge 20 has a top molding 44 and a removable protectivecover 42. The top molding 44 has a central web for structural stiffnessand to provide textured grip surfaces 58 for manipulating the cartridgeduring insertion and removal. The base portion of the protective cover42 protects the printhead ICs 100 and line of contacts 146 prior toinstallation in the printer. Caps 56 are integrally formed with the baseportion and cover ink inlets and outlets (see 54 and 52 of FIG. 12).

FIG. 11 shows the printhead cartridge 20 with its protective cover 42removed to expose the printhead ICs 100 (not shown in FIG. 11) on abottom surface and the line of contacts 146 on a side surface.

FIG. 12 is a partially exploded perspective of the printhead assembly20. The top cover 44 has been removed to reveal the inlet manifold 48and the outlet manifold 50. The inlet and outlet shrouds 46 and 47 havebeen removed to expose the five inlet and outlet spouts (52 and 54). Theinlet and outlet manifolds 48 and 50 form a fluid connection betweeneach of the individual inlets and outlets and a corresponding mainchannel (see 126 in FIG. 7) in the LCP channel molding 124.

FIG. 13 shows a print engine 30 of the type that uses the printheadcartridge 20. The print engine 30 is the internal structure of an inkjetprinter and therefore does not include any external casing, ink tanks ormedia feed and collection trays. The printhead cartridge 20 is insertedand removed by the user lifting and lowering a latch 26. The printengine 30 forms an electrical connection with 146 contacts on theprinthead cartridge 20. The print engine forms a fluid coupling via aninlet socket 32 and an outlet socket 33, which are connected to theinlet manifold 48 and outlet manifold 50 of the printhead cartridge 20.

FIG. 14 shows the print engine 30 with the printhead cartridge removedto reveal the apertures 34 in each of the sockets 32 and 33. Eachaperture 34 receives one of the spouts 52 (see FIG. 12) on the inlet andoutlet manifolds. Ink tanks have an arbitrary position and configurationbut simply connect to hollow spigots 124 (not shown) at the rear of thesockets 32 in the inlet coupling. A spigot at the rear of socket in theoutlet coupling 33 leads to a downstream ink line.

Connections of ink tanks to the inlet spouts 52 of the inlet manifold 48(via the inlet socket 32) determine the plumbing arrangement of colorplanes in the printhead. For example, one black ink tank may supply inkto two inlet spouts 52 of the inlet manifold 48 so as to provide twoblack color planes in the printhead. Alternatively, each black colorplane of the printhead may have a respective black ink tank.

FIG. 15 shows the print engine 30 with an installed bank ofuser-replaceable ink tanks 38 and corresponding pressure-regulatingchambers 39 for regulation of a hydrostatic pressure of ink supplied tothe printhead. Although fluidic connections between the variouscomponents are not shown in FIG. 15, it will be appreciated that theseconnections are made with suitable hoses in accordance with the fluidicssystem described in, for example, U.S. application Ser. No. 12/062,514,the contents of which are herein incorporated by reference.

FIG. 16 shows schematically a fluidics system 200 of the printer engineshown in FIG. 15. The pressure-regulating chamber 39 supplies ink 204 tothe ink inlet 48 of the printhead cartridge 20 via an upstream ink line234. The pressure-regulating chamber 39 is positioned below theprinthead cartridge 20 and maintains a predetermined set level 210 ofink therein by means of a float valve 216.

Ink 204 is supplied to the pressure-regulating chamber 39 by the inktank 38 positioned at any height h above the set level 210. The ink tank38 is typically a user-replaceable ink cartridge, which connects with anink supply line 230 when installed in the printer. The ink supply line230 provides fluidic communication between the ink reservoir 38 and aninlet port of the pressure-regulating chamber 39.

The ink outlet 50 of the printhead cartridge 20 is connected to adownstream ink line 238, which feeds back to a return port of thechamber 39. The downstream ink line comprises an inline a filter 282 andink pump 240 for controlling priming and de-priming operations.

Inkjet Inks

The inks utilized in the present invention are typically dye-based orpigment-based aqueous inkjet inks.

Inkjet dyes will be well-known to the person skilled in the art and thepresent invention is not limited to any particular type of dye. By wayof example, dyes suitable for use in the present invention include azodyes (e.g. Food Black 2), metal complex dyes, naphthol dyes,anthraquinone dyes, indigo dyes, carbonium dyes, quinone-imine dyes,xanthene dyes, cyanine dyes, quinoline dyes, nitro dyes, nitroso dyes,benzoquinone dyes, naphthoquinone dyes, phthalocyanine dyes (includingnaphthalocyanine dyes), and metal phthalocyanine dyes (including metalnaphthalocyanine dyes, such as those described in U.S. Pat. No.7,148,345, the contents of which is herein incorporated by reference).

Examples of suitable dyes include: CI Direct Black 4, 9, 11, 17, 19, 22,32, 80, 151, 154, 168, 171, 194 and 195; CI Direct Blue 1, 2, 6, 8, 22,34, 70, 71, 76, 78, 86, 142, 199, 200, 201, 202, 203, 207, 218, 236 and287; CI Direct Red 1, 2, 4, 8, 9, 11, 13, 15, 20, 28, 31, 33, 37, 39,51, 59, 62, 63, 73, 75, 80, 81, 83, 87, 90, 94, 95, 99, 101, 110, 189,225 and 227; CI Direct Yellow 1, 2, 4, 8, 11, 12, 26, 27, 28, 33, 34,41, 44, 48, 86, 87, 88, 132, 135, 142 and 144; CI Food Black 1 and 2; CIAcid Black 1, 2, 7, 16, 24, 26, 28, 31, 48, 52, 63, 107, 112, 118, 119,121, 172, 194 and 208; CI Acid Blue 1, 7, 9, 15, 22, 23, 27, 29, 40, 43,55, 59, 62, 78, 80, 81, 90, 102, 104, 111, 185 and 254; CI Acid Yellow1, 3, 4, 7, 11, 12, 13, 14, 19, 23, 25, 34, 38, 41, 42, 44, 53, 55, 61,71, 76 and 79; CI Reactive Blue 1, 2, 3, 4, 5, 6, 7, 8, 9, 13, 14, 15,17, 18, 19, 20, 21, 25, 26, 27, 28, 29, 31, 32, 33, 34, 37, 38, 39, 40,41, 43, 44 and 46; CI Reactive Red 1, 2, 3, 4, 5, 6, 7, 8, 11, 12, 13,15, 16, 17, 19, 20, 21, 22, 23, 24, 28, 29, 31, 32, 33, 34, 35, 36, 37,38, 39, 40, 41, 42, 43, 44, 45, 46, 49, 50, 58, 59, 63, 64, and 180; CIReactive Yellow 1, 2, 3, 4, 6 7, 11, 12, 13, 14, 15, 16, 17, 18, 22, 23,24, 25, 26, 27, 37 and 42; CI Reactive Black 1, 3, 4, 5, 6, 8, 9, 10,12, 13, 14 and 18; Pro-Jet® Fast Cyan 2 (Fujifilm Imaging Colorants);Pro-Jet® Fast Magenta 2 (Fujifilm Imaging Colorants); Pro-Jet® FastYellow 2 (Fujifilm Imaging Colorants); and Pro-Jet® Fast Black 2(Fujifilm Imaging Colorants)

Conventional pigments suitable for use in the present invention may beinorganic pigments or organic pigments. Examples of conventionalpigments are carbon black, Cadmium Red, Molybdenum Red, Chrome Yellow,Cadmium Yellow, Titan Yellow, chromium oxide, Viridian, Titan CobaltGreen, Ultramarine Blue, Prussian Blue, Cobalt Blue,diketopyrrolo-pyrrole, anthraquinone, benzimidazolone, anthrapyrimidine,azo pigments, phthalocyanine pigments (including naphthlocyaninepigments), uinacridone pigments, isoindolinone pigments, dioxazinepigments, indanthrene pigments, perylene pigments, perinone pigments,thioindigo pigments, quinophthalone pigments, and metal complexpigments.

Examples of suitable pigments include: Cyan COJ450 (Cabot), D71C andD75C (Diamond Dispersions); Magenta COJ465 (Cabot), D71M, D75M, D71PV19(Diamond Dispersions), Hostajet Magenta E-PT VP2690 and Hostajet MagentaE5B-PT VP3565 (Clariant); Yellow COJ270 and COJ470 (Cabot), or D71Y,D71Y155, D75Y (Diamond Dispersions) and Hostajet Yellow 4G-PT VP2669(Clariant); Black CW1, CW2, CW3 (Orient) or COJ200, COJ300, COJ400(Cabot) or SDP1000, SDP2000 (Sensient), or D71K, D75K, D77K, D80K(Diamond Dispersions) and Hostajet Black O-PT (Clariant); Red D71R(Diamond Dispersions); Blue D71B (Diamond Dispersions)

Typically, the pigments are self-dispersing pigments, such assurface-modified pigments. The surface modification may be eitheranionic group or a cationic. Typical surface-modifying groups arecarboxylate and sulfonate groups. However, other surface-modifyinggroups may also be used, such as anionic phosphate groups or cationicammonium groups.

Specific examples of suitable aqueous surface-modified pigmentdispersions for use in the present invention are Sensijet® Black SDP2000 (available from Sensient Colors Inc.) and CAB-O-JET® 200, 300,250C, 260M and 270Y (available from Cabot Corporation).

The average particle size of pigment particles in inkjet inks isoptionally in the range of 50 to 500 nm.

Pigments and dyes may be used in inkjet inks either individually or as acombination of two or more thereof.

Ink vehicles for inkjet inks will be well known to the person skilled inthe art and the ink vehicles used in the present invention are notparticularly limited. The ink vehicles used in the present invention aretypically conventional aqueous ink vehicles comprising at least 40 wt %water, at least 50 wt % water or at least 60 wt % water. Usually, theamount of water present in the inkjet ink is in the range of 50 wt % to90 wt %, or optionally in the range of 60 wt % to 80 wt %.

Aqueous inkjet inks compositions are well known in the literature and,in addition to water, may comprise other components, such as co-solvents(including humectants, penetrants, wetting agents etc.), surfactants,biocides, sequestering agents, pH adjusters, viscosity modifiers, etc.

Co-solvents are typically water-soluble organic solvents. Suitablewater-soluble organic solvents include C₁₋₄ alkyl alcohols, such asethanol, methanol, butanol, propanol, and 2-propanol; glycol ethers,such as ethylene glycol monomethyl ether, ethylene glycol monoethylether, ethylene glycol monobutyl ether, ethylene glycol monomethyl etheracetate, diethylene glycol monomethyl ether, diethylene glycol monoethylether, diethylene glycol mono-n-propyl ether, ethylene glycolmono-isopropyl ether, diethylene glycol mono-isopropyl ether, ethyleneglycol mono-n-butyl ether, diethylene glycol mono-n-butyl ether,triethylene glycol mono-n-butyl ether, ethylene glycol mono-t-butylether, diethylene glycol mono-t-butyl ether, 1-methyl-1-methoxybutanol,propylene glycol monomethyl ether, propylene glycol monoethyl ether,propylene glycol mono-t-butyl ether, propylene glycol mono-n-propylether, propylene glycol mono-isopropyl ether, dipropylene glycolmonomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycolmono-n-propyl ether, dipropylene glycol mono-isopropyl ether, propyleneglycol mono-n-butyl ether, and dipropylene glycol mono-n-butyl ether;formamide, acetamide, dimethyl sulfoxide, sorbitol, sorbitan, glycerolmonoacetate, glycerol diacetate, glycerol triacetate, and sulfolane; orcombinations thereof.

Other useful water-soluble organic solvents, which may be used asco-solvents, include polar solvents, such as 2-pyrrolidone,N-methylpyrrolidone, ε-caprolactam, dimethyl sulfoxide, sulfolane,morpholine, N-ethylmorpholine, 1,3-dimethyl-2-imidazolidinone andcombinations thereof.

The inkjet ink may contain a high-boiling water-soluble organic solventas a co-solvent, which can serve as a wetting agent or humectant forimparting water retentivity and wetting properties to the inkcomposition. Such a high-boiling water-soluble organic solvent includesone having a boiling point of 180° C. or higher. Examples of thewater-soluble organic solvent having a boiling point of 180° C. orhigher are ethylene glycol, propylene glycol, diethylene glycol,pentamethylene glycol, trimethylene glycol, 2-butene-1,4-diol,2-ethyl-1,3-hexanediol, 2-methyl-2,4-pentanediol, tripropylene glycolmonomethyl ether, dipropylene glycol monoethyl glycol, dipropyleneglycol monoethyl ether, dipropylene glycol monomethyl ether, dipropyleneglycol, triethylene glycol monomethyl ether, tetraethylene glycol,triethylene glycol, diethylene glycol monobutyl ether, diethylene glycolmonoethyl ether, diethylene glycol monomethyl ether, tripropyleneglycol, polyethylene glycols having molecular weights of 2000 or lower,1,3-propylene glycol, isopropylene glycol, isobutylene glycol,1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol,glycerol, erythritol, pentaerythritol and combinations thereof.

Other suitable wetting agents or humectants include saccharides(including monosaccharides, oligosaccharides and polysaccharides) andderivatives thereof (e.g. maltitol, sorbitol, xylitol, hyaluronic salts,aldonic acids, uronic acids etc.)

The inkjet ink may also contain a penetrant, as one of the co-solvents,for accelerating penetration of the aqueous ink into the recordingmedium. Suitable penetrants include polyhydric alcohol alkyl ethers(glycol ethers) and/or 1,2-alkyldiols. Examples of suitable polyhydricalcohol alkyl ethers are ethylene glycol monomethyl ether, ethyleneglycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycolmonomethyl ether acetate, diethylene glycol monomethyl ether, diethyleneglycol monoethyl ether, ethylene glycol mono-n-propyl ether, ethyleneglycol mono-isopropyl ether, diethylene glycol mono-isopropyl ether,ethylene glycol mono-n-butyl ether, diethylene glycol mono-n-butylether, triethylene glycol mono-n-butyl ether, ethylene glycolmono-t-butyl ether, diethylene glycol mono-t-butyl ether,1-methyl-1-methoxybutanol, propylene glycol monomethyl ether, propyleneglycol monoethyl ether, propylene glycol mono-t-butyl ether, propyleneglycol mono-n-propyl ether, propylene glycol mono-isopropyl ether,dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether,dipropylene glycol mono-n-propyl ether, dipropylene glycolmono-isopropyl ether, propylene glycol mono-n-butyl ether, anddipropylene glycol mono-n-butyl ether. Examples of suitable1,2-alkyldiols are 1,2-pentanediol and 1,2-hexanediol. The penetrant mayalso be selected from straight-chain hydrocarbon diols, such as1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol,1,7-heptanediol, and 1,8-octanediol. Glycerol may also be used as apenetrant.

Typically, the amount of co-solvent present in the ink is in the rangeof about 5 wt % to 40 wt %, or optionally 10 wt % to 30 wt %. A specificexample of a co-solvent system, which may be used in the presentinvention, comprises ethylene glycol, 2-pyrrolidone, glycerol and1-propanol.

The inkjet ink may also contain one or more surface active agents(“surfactant”), such as an anionic surface active agent, a zwitterionicsurface active agent, a nonionic surface active agent or mixturesthereof. Useful anionic surface active agents include sulfonic acidtypes, such as alkanesulfonic acid salts, α-olefinsulfonic acid salts,alkylbenzenesulfonic acid salts, alkylnaphthalenesulfonic acids,acylmethyltaurines, and dialkylsulfosuccinic acids; alkylsulfuric estersalts, sulfated oils, sulfated olefins, polyoxyethylene alkyl ethersulfuric ester salts; carboxylic acid types, e.g., fatty acid salts andalkylsarcosine salts; and phosphoric acid ester types, such asalkylphosphoric ester salts, polyoxyethylene alkyl ether phosphoricester salts, and glycerophosphoric ester salts. Specific examples of theanionic surface active agents are sodium dodecylbenzenesulfonate, sodiumlaurate, and a polyoxyethylene alkyl ether sulfate ammonium salt.

Examples of zwitterionic surface active agents includeN,N-dimethyl-N-octyl amine oxide, N,N-dimethyl-N-dodecyl amine oxide,N,N-dimethyl-N-tetradecyl amine oxide, N,N-dimethyl-N-hexadecyl amineoxide, N,N-dimethyl-N-octadecyl amine oxide andN,N-dimethyl-N-(Z-9-octadecenyl)-N-amine oxide.

Examples of nonionic surface active agents include ethylene oxide adducttypes, such as polyoxyethylene alkyl ethers, polyoxyethylene alkylphenylethers, polyoxyethylene alkyl esters, and polyoxyethylene alkylamides;polyol ester types, such as glycerol alkyl esters, sorbitan alkylesters, and sugar alkyl esters; polyether types, such as polyhydricalcohol alkyl ethers; and alkanolamide types, such as alkanolamine fattyacid amides. Specific examples of nonionic surface active agents areethers such as polyoxyethylene nonylphenyl ether, polyoxyethyleneoctylphenyl ether, polyoxyethylene dodecylphenyl ether, polyoxyethylenealkylallyl ether, polyoxyethylene oleyl ether, polyoxyethylene laurylether, and polyoxyalkylene alkyl ethers (e.g. polyoxyethylene alkylethers); and esters, such as polyoxyethylene oleate, polyoxyethyleneoleate ester, polyoxyethylene distearate, sorbitan laurate, sorbitanmonostearate, sorbitan mono-oleate, sorbitan sesquioleate,polyoxyethylene mono-oleate, and polyoxyethylene stearate. Acetyleneglycol surface active agents, such as2,4,7,9-tetramethyl-5-decyne-4,7-diol; ethoxylated2,4,7,9-tetramethyl-5-decyne-4,7-diol; 3,6-dimethyl-4-octyne-3,6-diol or3,5-dimethyl-1-hexyn-3-ol, may also be used. Specific examples ofnonionic surfactants, which may be used in the present invention, areSurfynol® 465 and Surfynol® 440 (available from Air Products andChemicals, Inc)

The surfactant(s) are typically present in the aqueous inkjet ink in anamount ranging from 0.1 wt % to 2 wt %. As described above, the amountof surfactant in relatively low luminance inks is at least 0.4 wt. %greater than the amount of surfactant in relatively high luminance inks.Typically, color inks have at least 0.4 wt. % more surfactant than blackink in a given ink set.

The aqueous inkjet ink may also include a pH adjuster or buffer, such assodium hydroxide, potassium hydroxide, lithium hydroxide, sodiumcarbonate, sodium hydrogencarbonate, potassium carbonate, potassiumhydrogencarbonate, lithium carbonate, sodium phosphate, potassiumphosphate, lithium phosphate, potassium dihydrogenphosphate, dipotassiumhydrogenphosphate, sodium oxalate, potassium oxalate, lithium oxalate,sodium borate, sodium tetraborate, potassium hydrogenphthalate, andpotassium hydrogentartrate; ammonia; and amines, such as methylamine,ethylamine, diethylamine, trimethylamine, triethylamine,tris(hydroxymethyl)aminomethane hydrochloride, triethanolamine,diethanolamine, diethylethanolamine, triisopropanolamine,butyldiethanolamine, morpholine, propanolamine,4-morpholineethanesulfonic acid and 4-morpholinepropanesulfonic acid(“MOPS”). The amount of pH adjuster, when present, is typically in therange of from 0.01 to 2 wt. % or 0.05 to 1 wt. %.

The aqueous inkjet ink may also include a biocide, such as benzoic acid,dichlorophene, hexachlorophene, sorbic acid, hydroxybenzoic esters,sodium dehydroacetate, 1,2-benthiazolin-3-one (“Proxel® GXL”, availablefrom Arch Chemicals, Inc.), 3,4-isothiazolin-3-one or4,4-dimethyloxazolidine. The amount of pH adjuster, when present, istypically in the range of from 0.01 to 2 wt. % or 0.05 to 1 wt. %.

The aqueous inkjet ink may also contain a sequestering agent, such asethylenediaminetetraacetic acid (EDTA).

Experimental Section

The following experimental section demonstrates the problems of adversecolor mixing on nozzle plates of Memjet® printheads, and furtherdemonstrates the advantages of particular ink sets in combination withprinthead plumbing configurations optimized for minimizing adverse colormixing.

A number of different ink sets, each containing CMYK inks, were preparedfor testing. Each ink was formulated by mixing ink vehicle components ina glass bottle and stirring for 24 hours. The ink vehicles were added torequisite colorants, stirred for a further 15 minutes, and thenfiltered. Both dye-based and pigment-based ink sets were prepared. Theink sets had the following formulations:

Ink Set 1 1Y 1K 1C 1M Ethylene glycol 10 parts 10 parts 10 parts 10parts 2-pyrrolidinone 9 parts 9 parts 9 parts 9 parts Glycerol 3 parts 3parts 3 parts 3 parts 1-Propanol 3 parts 3 parts 3 parts 3 parts Yellowdye 4 parts Black dye 6 parts Cyan dye 5 parts Magenta dye 4 partsSurfynol 465 1.0 parts 0.2 parts 1.0 parts 1.0 parts Proxel GXL 0.2parts 0.2 parts 0.2 parts 0.2 parts MOPS 0.2 parts 0.2 parts 0.2 parts0.2 parts Water To 100 parts To 100 parts To 100 parts To 100 partsSurface Tension at 33.4 39.7 34.1 37.4 25° C. (mN/m)

Ink Set 2 2Y 2K 2C 2M Ethylene glycol 10 parts 13 parts 10 parts 10parts 2-pyrrolidinone 9 parts 9 parts 9 parts 9 parts Glycerol 3 parts3.2 parts 3 parts 3 parts 1-Propanol 3 parts 3 parts 3 parts 3 partsYellow dye 4 parts Black dye 6 parts Cyan dye 5 parts Magenta dye 4parts Surfynol 465 0.8 parts 0.2 parts 0.8 parts 0.8 parts Proxel GXL0.2 parts 0.2 parts 0.2 parts 0.2 parts MOPS 0.2 parts 0.2 parts 0.2parts 0.2 parts Water To 100 parts To 100 parts To 100 parts To 100parts Surface Tension at 33.1 39.7 34.0 37.4 25° C. (mN/m)

Ink Set 3 3Y 3K 3C 3M Ethylene glycol 10 parts 10 parts 10 parts 10parts 2-pyrrolidinone 9 parts 9 parts 9 parts 9 parts Glycerol 3 parts 3parts 3 parts 3 parts Yellow pigment 5 parts Black pigment 5 parts Cyanpigment 3.5 parts Magenta pigment 5 parts Surfynol 465 1.0 parts 0.2parts 1.0 parts 1.0 parts Water To 100 parts To 100 parts To 100 partsTo 100 parts Surface Tension at 33.1 40.8 34.2 35.5 25° C. (mN/m)

Comparative Ink Set 1 Comp 1Y Comp 1K Comp 1C Comp 1M Ethylene glycol 10parts 25 parts 10 parts 10 parts 2-pyrrolidinone 9 parts 9 parts 9 partsGlycerol 3 parts 3 parts 3 parts 1-Propanol 3 parts 3 parts 3 partsYellow dye 4 parts Black dye 6 parts Cyan dye 5 parts Magenta dye 4parts Surfynol 465 1.0 parts 0.2 parts 1.0 parts Proxel GXL 0.2 parts0.2 parts 0.2 parts 0.2 parts MOPS 0.2 parts 0.2 parts 0.2 parts 0.2parts Water To 100 parts To 100 parts To 100 parts To 100 parts SurfaceTension at 33.4 63.5 39.7 38.7 25° C. (mN/m)

Comparative Ink Set 2 Comp 2Y Comp 2K Comp 2C Comp 2M Ethylene glycol 10parts 10 parts 10 parts 10 parts 2-pyrrolidinone 9 parts 9 parts 9 parts9 parts Glycerol 3 parts 3 parts 3 parts 3 parts 1-Propanol 3 parts 3parts 3 parts 3 parts Yellow dye 4 parts Black dye 6 parts Cyan dye 5parts Magenta dye 4 parts Surfynol 465 0.2 parts 0.2 parts 0.2 parts 1.0parts Proxel GXL 0.2 parts 0.2 parts 0.2 parts 0.2 parts MOPS 0.2 parts0.2 parts 0.2 parts 0.2 parts Water To 100 parts To 100 parts To 100parts To 100 parts Surface Tension at 38.8 39.7 38.6 37.4 25° C. (mN/m)

Comparative Ink Set 3 Comp 3Y Comp 3K Comp 3C Comp 3M Ethylene glycol 10parts 13 parts 10 parts 10 parts 2-pyrrolidinone 9 parts 9 parts 9 parts9 parts Glycerol 3 parts 3.2 parts 3 parts 3 parts Yellow dye 4 partsBlack dye 6 parts Cyan dye 5 parts Magenta dye 4 parts Surfynol 465 0.2parts 0.2 parts 0.2 parts 1.0 parts Proxel GXL 0.2 parts 0.2 parts 0.2parts 0.2 parts MOPS 0.2 parts 0.2 parts 0.2 parts 0.2 parts Water To100 parts To 100 parts To 100 parts To 100 parts Surface Tension at 38.740.5 38.9 39.8 25° C. (mN/m)

Comparative Ink Set 4 Comp 4Y Comp 4K Comp 4C Comp 4M Ethylene glycol 10parts 10 parts 10 parts 10 parts 2-pyrrolidinone 9 parts 9 parts 9 parts9 parts Glycerol 3 parts 3 parts 3 parts 3 parts Yellow pigment 5 partsBlack pigment 5 parts Cyan pigment 3.5 parts Magenta pigment 5 partsSurfynol 465 0.5 parts 0.2 parts 0.5 parts 0.5 parts Water To 100 partsTo 100 parts To 100 parts To 100 parts Surface Tension at 38.2 40 36.940.4 25° C. (mN/m)

The four inks from each ink set were plumbed into a Memjet® printhead soas to supply color planes 1, 2, 3, 4 and 5. In each case, the ink setswere plumbed into the color planes in the order shown in Table 1:

TABLE 1 Printhead Plumbing Configuration for CMYK ink sets Color ColorColor Color Color Plane 1 Plane 2 Plane 3 Plane 4 Plane 5 Yellow (Y)Black (K) Cyan (C) Black (K) Magenta (M)

A nozzle check pattern of color planes 1-5 was printed to ensure theprinthead was primed. Test patterns were then printed to stress eachcolor plane and analyze any color mixing that had occurred inneighboring color planes from the stressed color plane. Typically, acolor plane is stressed by printing at full bleed from that color plane,and then nozzle check patterns printed sequentially from each of thecolor planes 1-5 of the printhead. Thus, a typical test pattern whichstresses a black color plane may comprise a black shape (e.g. rectangleor triangle) printed at full bleed to cover most of an A4 sheet, andfive lines of yellow, black, cyan, black and magenta (about 1 mm inwidth) printed immediately below the black shape. Mixing of colorplane(s) in the printhead is determined by visually inspecting thenozzle check patterns (10× magnification) as well as the printheadnozzle face. Ink mixing is deemed to occur if ink from a stressed colorplane has migrated into neighboring color plane(s). For example, if anyof the lines of yellow, cyan and magenta in the test pattern containstreaks of black, then adverse color mixing on the nozzle face is deemedto have occurred.

The results color mixing experiments are shown in Tables 2-8 below. InTables 2-8, each column header of the table shows the stressed colorplane and each row of the table shows a neighboring color plane (if any)into which the stressed color plane has mixed during the experiment. Byway of nomenclature, a ‘0’ indicates no color mixing and ‘X’ indicatescolor mixing.

TABLE 2 Analysis of Ink Set 1 Stressed color plane Mixing color plane 12 3 4 5 1 N/A 0 0 0 0 2 0 N/A X 0 0 3 0 0 N/A 0 0 4 0 0 0 N/A X 5 0 0 00 N/A

For Ink Set 1, no color mixing was observed from either of the blackcolor planes 2 and 4 into neighboring color planes. The only colormixing observed was from the magenta color plane 5 into the neighboringblack color plane 4, and from the cyan color plane 3 into theneighboring black color plane 2. This color mixing is considered to beacceptable, because it does not adversely affect the visual appearanceof printed black dots.

TABLE 3 Analysis of Ink Set 2 Stressed color plane Mixing color plane 12 3 4 5 1 N/A 0 0 0 0 2 X N/A X 0 0 3 0 0 N/A 0 0 4 0 0 X N/A X 5 0 0 00 N/A

TABLE 4 Analysis of Ink Set 3 Stressed color plane Mixing color plane 12 3 4 5 1 N/A 0 0 0 0 2 X N/A X 0 0 3 0 0 N/A 0 0 4 0 0 X N/A X 5 0 0 00 N/A

For Ink Sets 2 and 3, no color mixing was observed from either of theblack color planes 2 and 4 into neighboring color planes. Color mixingobserved was from the magenta color plane 5 into the neighboring blackcolor plane 4, from the cyan color plane 3 into both neighboring blackcolor planes 2 and 4, and from the yellow color plane into theneighboring black color plane 2. This color mixing is considered to beacceptable, because it does not adversely affect the visual appearanceof printed black dots.

TABLE 5 Analysis of Comparative Ink Set 1 Stressed color plane Mixingcolor plane 1 2 3 4 5 1 N/A 0 0 0 0 2 X N/A X 0 0 3 0 X N/A X 0 4 0 0 XN/A X 5 0 0 0 0 N/A

For Comparative Ink Set 1, color mixing was observed from both the blackcolor planes 2 and 4 into the neighboring cyan color plane 3. This colormixing was considered to be unacceptable, because the visual appearanceof printed cyan dots was adversely affected by mixing of the black ink.

TABLE 6 Analysis of Comparative Ink Set 2 Stressed color plane Mixingcolor plane 1 2 3 4 5 1 N/A X 0 0 0 2 X N/A X 0 0 3 0 X N/A X 0 4 0 0 XN/A X 5 0 0 0 0 N/A

TABLE 7 Analysis of Comparative Ink Set 3 Stressed color plane Mixingcolor plane 1 2 3 4 5 1 N/A X 0 0 0 2 X N/A X 0 0 3 0 X N/A X 0 4 0 0 XN/A X 5 0 0 0 0 N/A

For Comparative Ink Sets 2 and 3, color mixing was observed from boththe black color planes 2 and 4 into the neighboring cyan color plane 3.Color mixing was also observed from the black color plane 2 into theneighboring yellow color plane 1. This color mixing was considered to beunacceptable, because the visual appearance of printed cyan and yellowdots was adversely affected by mixing of the black ink.

TABLE 8 Analysis of Comparative Ink Set 4 Stressed color plane Mixingcolor plane 1 2 3 4 5 1 N/A X 0 0 0 2 X N/A X 0 0 3 0 X N/A X 0 4 0 0 XN/A X 5 0 0 0 X N/A

For Comparative Ink Set 4, color mixing was observed from both the blackcolor planes 2 and 4 into the neighboring cyan color plane 3. Colormixing was also observed from the black color plane 2 into theneighboring yellow color plane 1. Color mixing was also observed fromthe black color plane 4 into the neighboring magenta color plane 5. Thiscolor mixing was considered to be unacceptable, because the visualappearance of printed cyan, magenta and yellow dots was adverselyaffected by mixing of the black ink.

Conclusions

The results shown in Tables 2-8 demonstrate that color mixing iscontrolled by an amount of surfactant in each ink. In particular, mixingfrom black ink into neighboring color inks across the nozzle face of theprinthead is minimized only if the amount of surfactant in color inks isat least 0.4 wt. % (preferably at least 0.6 wt. %) greater than theamount of surfactant in the black ink.

Surprisingly, the surface tension of each ink appeared to be of lesserimportance in controlling the extent and direction of color mixing. Forexample, the black ink in Comparative Ink Set 1 has a high surfacetension of 63.5 mN/m. However, this high surface tension does notprevent black ink from color planes 2 and 4 mixing into cyan ink incolor plane 3, and thereby adversely affecting the visual appearance ofprinted cyan dots. Likewise, in each of the Comparative Ink Sets 2-4, arelatively higher surface tension of black ink does not prevent blackink from mixing into neighboring color plane(s). Accordingly, it wasconcluded that Marangoni effect does not predict color mixing across thenozzle face of a printhead; only the relative amounts of surfactant ineach ink were able to control the extent and direction of color mixingacross the nozzle face.

The ink sets described herein together with optimized printhead plumbingarrangements provide improved print quality in multi-color printheads byminimizing adverse color mixing between closely spaced color planes inthe printhead.

It will, of course, be appreciated that the present invention has beendescribed by way of example only and that modifications of detail may bemade within the scope of the invention as defined in the claims appendedhereto.

1-20. (canceled)
 21. An inkjet printer comprising an inkjet printheadpositioned relative to a media feed direction, said printhead comprisinga plurality of color planes for ejecting different inks, each colorplane comprising at least one nozzle row defined in a nozzle face ofsaid printhead, each nozzle in a respective color plane being suppliedwith a same ink, wherein said printhead is plumbed such that a firstcolor plane positioned furthest upstream with respect to the media feeddirection ejects yellow ink and a second color plane neighboring thefirst color plane ejects black ink.
 22. The inkjet printer of claim 21comprising at least two color planes ejecting black ink.
 23. The inkjetprinter of claim 22, wherein each color plane ejecting a non-black inkhas at least one neighboring color plane ejecting a black ink.
 24. Theinkjet printer of claim 22, wherein a third color plane ejecting anon-black ink is sandwiched between a pair of color planes ejectingblack ink
 25. The printer of claim 21, wherein a distance between nozzlerows from neighboring color planes is less than 200 microns.
 26. Theprinter of claim 21, wherein the printhead is plumbed such that colorplanes across the nozzle face have an alternating sequence of non-blackand black inks.
 27. The printer of claim 21, wherein the yellow inkcontains a greater amount of surfactant than the black ink.
 28. Theprinter of claim 27, wherein the yellow ink contains at least 0.4 wt. %more surfactant than the black ink.